Various types of surgical procedures are currently performed to investigate, diagnose, and treat diseases of the heart and the great vessels of the thorax. Such procedures include repair and replacement of mitral, aortic, and other heart valves, repair of atrial and ventricular septal defects, pulmonary thrombectomy, treatment of aneurysms, electrophysiological mapping and ablation of the myocardium, and other procedures in which interventional devices are introduced into the interior of the heart or a great vessel.
Using current techniques, many of these procedures require a gross thoracotomy, usually in the form of a median sternotomy, to gain access into the patient's thoracic cavity. A saw or other cutting instrument is used to cut the sternum longitudinally, allowing two opposing halves of the anterior or ventral portion of the rib cage to be spread apart. A large opening into the thoracic cavity is thus created, through which the surgical team may directly visualize and operate upon the heart and other thoracic contents.
Surgical intervention within the heart generally requires isolation of the heart and coronary blood vessels from the remainder of the arterial system, and arrest of cardiac function. Usually, the heart is isolated from the arterial system by introducing an external aortic crossclamp through a sternotomy and applying it to the aorta between the brachiocephalic artery and the coronary ostia. Cardioplegic fluid is then injected into the coronary arteries, either directly into the coronary ostia or through a puncture in the aortic root, so as to arrest cardiac function. In some cases, cardioplegic fluid is injected into the coronary sinus for retrograde perfusion of the myocardium. The patient is placed on cardiopulmonary bypass to maintain peripheral circulation of oxygenated blood.
Of particular interest to the present invention are intracardiac procedures for surgical treatment of heart valves, especially the mitral and aortic valves. According to recent estimates, more than 79,000 patients are diagnosed with aortic and mitral valve disease in U.S. hospitals each year. More than 49,000 mitral valve or aortic valve replacement procedures are performed annually in the U.S., along with a significant number of heart valve repair procedures.
Various surgical techniques may be used to repair a diseased or damaged valve, including annuloplasty (contracting the valve annulus), quadrangular resection (narrowing the valve leaflets), commissurotomy (cutting the valve commissures to separate the valve leaflets), shortening mitral or tricuspid valve chordae tendonae, reattachment of severed mitral or tricuspid valve chordae tendonae or papillary muscle tissue, and decalcification of valve and annulus tissue. Alternatively, the valve may be replaced, by excising the valve leaflets of the natural valve, and securing a replacement valve in the valve position, usually by suturing the replacement valve to the natural valve annulus. Various types of replacement valves are in current use, including mechanical and biological prostheses, homografts, and allografts, as described in Bodnar and Frater, Replacement Cardiac Valves 1-357 (1991), which is incorporated herein by reference. A comprehensive discussion of heart valve diseases and the surgical treatment thereof is found in Kirklin and Barratt-Boyes, Cardiac Surgery 323-459 (1986), the complete disclosure of which is incorporated herein by reference.
The mitral valve, located between the left atrium and left ventricle of the heart, is most easily reached through the wall of the left atrium, which normally resides on the posterior side of the heart, opposite the side of the heart that is exposed by a median sternotomy. Therefore, to access the mitral valve via a sternotomy, the heart is rotated to bring the left atrium into an anterior position accessible through the sternotomy. An opening, or atriotomy, is then made in the right side of the left atrium, anterior to the right pulmonary veins. The atriotomy is retracted by means of sutures or retraction devices, exposing the mitral valve directly posterior to the atriotomy. One of the aforementioned techniques may then be used to repair or replace the valve.
An alternative technique for mitral valve access may be used when a median sternotomy and/or rotational manipulation of the heart are undesirable. In this technique, a large incision is made in the right lateral side of the chest, usually in the region of the fourth intercostal space. One or more ribs may be removed from the patient, and other ribs near the incision are retracted outward to create a large opening into the thoracic cavity. The left atrium is then exposed on the posterior side of the heart, and an atriotomy is formed in the wall of the left atrium, through which the mitral valve may be accessed for repair or replacement.
Using such open-chest techniques, the large opening provided by a median sternotomy or right thoracotomy enables the surgeon to see the mitral valve directly through the left atriotomy, and to position his or her hands within the thoracic cavity in close proximity to the exterior of the heart for manipulation of surgical instruments, removal of excised tissue, and/or introduction of a replacement valve through the atriotomy for attachment within the heart. However, these invasive, open-chest procedures produce a high degree of trauma, a significant risk of complications, an extended hospital stay, and a painful recovery period for the patient. Moreover, while heart valve surgery produces beneficial results for many patients, numerous others who might benefit from such surgery are unable or unwilling to undergo the trauma and risks of current techniques.
In response to the various problems associated with open-chest procedures, new methods of performing closed-chest surgery on the heart using minimally invasive thoracoscopic techniques have been recently developed. In these methods, the patient's heart is arrested by occluding the patient's aorta between the coronary arteries and the brachiocephalic artery with an expandable balloon on the distal end of an endovascular catheter introduced via a femoral artery. Cardioplegic fluid is then delivered to the patient's myocardium through a lumen in the same catheter or through a catheter positioned in the coronary sinus via a peripheral vein. To repair or replace the mitral valve, minimally-invasive cutting and suturing instruments are then introduced thoracoscopically through a trocar sleeve in the right lateral portion of the chest. A complete description of such methods is found in commonly assigned, co-pending application Ser. No. 08/163,241, filed Dec. 6, 1993, which is incorporated herein by reference.
This new generation of thoracoscopic methods of performing heart valve repair has, of course, created many new challenges. One such challenge is that of retracting the left atrial wall to open the atriotomy so that the mitral valve can be exposed for the surgical procedure. The heart wall must be retracted anteriorly to suitably expose the mitral valve and provide access through the atriotomy for the cutting and suturing instruments introduced through the right lateral portion of the chest. In addition, the instruments that retract the heart wall must be introduced in a minimally-invasive manner through small percutaneous incisions or cannulae positioned in intercostal spaces in the patient's rib cage.
Introducing an instrument through an intercostal space in the anterior side of the chest presents additional problems. One such problem is that the patient's rib cage is typically structured so that the ribs in the anterior portion of the chest are closer together than in the lateral portions of the chest. In addition, the tissue layer in the anterior chest wall contains nerves that could be damaged by a large percutaneous incision. Therefore, a retraction device introduced from the anterior side should be as small as possible, preferably on the order of 3-8 mm, to fit within the smaller anterior intercostal spaces and to avoid unnecessary trauma to the patient. Another problem is that the part of the retraction device that engages the heart wall must be wide enough to engage a sufficient portion of the heart wall to open the atriotomy enough to expose the mitral valve. It must also be long enough to extend a sufficient distance into the heart to extend beneath the interatrial septum and prevent it from sagging or otherwise inhibiting access to the mitral valve. Introducing an instrument which is large enough to sufficiently expose the mitral valve through the smaller intercostal spaces in the anterior portion of the chest is problematic.
What is needed, therefore, are improved systems and methods for manipulating a tissue structure in a body cavity via a small percutaneous incision or cannula. Preferably, the systems and methods would be capable of retracting an incision in a vessel or organ, such as an atriotomy in the left atrium to expose the mitral valve for repair or replacement. The system should be configured for introduction through an extremely small percutaneous penetration, such as a cannula positioned in an anterior intercosial space. The system should also be large enough to retract the heart wall sufficiently to expose the mitral valve and to support the interatrial septum. In addition, the system should be configured to facilitate retraction of the left atrium from the anterior side of the chest.